Electrodynamic actuator and electrodynamic excitation device

ABSTRACT

A linear actuator, comprising: a base; a fixed part support mechanism attached to the base; a fixed part elastically supported by the fixed part support mechanism; and a movable part driven to reciprocate in a predetermined drive direction with respect to the fixed part, wherein the fixed part support mechanism comprises: a movable block attached to the fixed part; a linear guide that couples the movable block with the base to be slidable in the predetermined drive direction; and an elastic member that is disposed between the base and the movable block and prevents transmission of a high frequency component of vibration in the predetermined drive direction.

This is a Continuation-in-Part of International Application No.PCT/JP2012/060581 filed Apr. 19, 2012, which claims priority fromJapanese Patent Applications Nos. 2011-098775 filed Apr. 26, 2011 and2011-238849 filed Oct. 31, 2011. The entire disclosure of the priorapplications is hereby incorporated by reference herein its entirety.

TECHNICAL FIELD

The present invention relates to an electrodynamic actuator and anelectrodynamic excitation device employing the electrodynamic actuator.

BACKGROUND

An electrodynamic excitation device employing a so-called voice coilmotor as a driving device is known. In PCT International Publication No.WO2009/130953 (hereafter, referred to as patent document 1), a triaxialexcitation device 1 in which three electrodynamic actuators 200, 300 and400 whose drive axes are oriented to perpendicularly intersect with eachother are coupled to a vibration table 100 is disclosed. In theexcitation device 1 described in the patent document 1, a drive shaft ofeach electrodynamic actuator is coupled to the vibration table 100 via abiaxial slider (joint parts 240, 340 and 440) which is slidable in twoaxes directions which are perpendicular to the drive axis. The biaxialslider 240 (340, 440) is configured by coupling a pair of linear guidesdisposed such that movable axes thereof are perpendicular to each other,via an intermediate stage 245 (345, 445). With this configuration, oneelectrodynamic actuator is able to drive the excitation table 100without being strongly affected by driving of the excitation table 100by the other electrodynamic actuators.

SUMMARY

However, in the electrodynamic actuator used in the excitation device 1of the patent document 1, a movable part 230 is supported by a fixedpart 222 only at a tip portion of a slender bar 234 protruding in adrive direction from one end off a body part 232. Therefore, the bodypart 232 of the movable part 230 is not supported at a high degree ofrigidity in regard to the direction perpendicular to the drivedirection, and therefore is easily vibrated in non-drive directions. Forthis reason, there is a case where crosstalk is caused between the driveaxes due to vibrations of the movable part 230 in the non-drivedirections and thereby the accuracy of excitation deteriorates.

The present invention is advantageous in that it provides anelectrodynamic actuator whose movable part is hard to vibrate in thenon-derive directions, and an electrodynamic excitation deviceconfigured to have an excellent accuracy of excitation by using such anelectrodynamic actuator.

According an aspect of the invention, there is provided a linearactuator, comprising: a base; a fixed part support mechanism attached tothe base; a fixed part elastically supported by the fixed part supportmechanism; and a movable part driven to reciprocate in a predetermineddrive direction with respect to the fixed part. The fixed part supportmechanism comprises: a movable block attached to the fixed part; alinear guide that couples the movable block with the base to be slidablein the predetermined drive direction; and an elastic member that isdisposed between the base and the movable block and preventstransmission of a high frequency component of vibration in thepredetermined drive direction.

Since the fixed part is fixed to the base via the fixed part supportmechanism, transmission of vibration in the axial direction to the fixedpart can be prevented.

The elastic member may comprise an air spring.

The linear actuator may further comprise a fixing block fixed to thebase. In this case, at least one of the linear guide and the elasticmember may be attached to the base via the fixing block.

The movable block may be provided as a pair of movable blocks. In thiscase, the pair of movable blocks may be attached to both side surfacesof the fixed part to sandwich an axis of the fixed part therebetween.

At least a part of the movable part may be accommodated in a cylindricalhollow part of the fixed part, thereby forming the linear actuator as anelectrodynamic actuator. The linear actuator may further comprise aplurality of movable part support mechanisms that support the movablepart from a lateral side to enable the movable part to reciprocate in anaxial direction of the fixed part. In this configuration, each of theplurality of movable part support mechanisms may comprise: a railattached to a side surface of the movable part to extend in thepredetermined drive direction; and a runner block attached to the fixedpart to engage with the rail. The plurality of movable part supportmechanisms may be arranged to have approximately constant intervalstherebetween around an axis of the fixed part.

The plurality of movable part support mechanisms may be two pairs ofmovable part support mechanisms. In this case, the movable part may bedisposed to be sandwiched between the two pairs of movable part supportmechanisms in two directions which are perpendicular to each other.

The linear actuator may be horizontally disposed in a state where theaxis of the fixed part is oriented in a horizontal direction. In thiscase, one of the plurality of movable part support mechanisms may bedisposed under the axis of the fixed part.

The movable part may comprise a rod extending along the axis of thefixed part to protrude from one end of the movable part. In this case,the fixed part may comprise a bearing which supports the rod to bemovable in the axial direction of the fixed part.

According to another aspect of the invention, there is provided anexcitation device, comprising: at least one linear actuator describedabove; and a vibration table coupled to the movable part of the at leastone linear actuator.

The at least one linear actuator may comprise two linear actuators. Inthis case, one of the two linear actuators may be a first actuatorhaving a driving axis in a first direction, and the other of the twolinear actuators may be a second actuator having a driving axis in asecond direction perpendicular to the first direction. The excitationdevice may further comprise: a first slider that couples the vibrationtable with the first actuator to be slidable in the second direction;and a second slider that couples the vibration table with the secondactuator to be slidable in the first direction.

The excitation device may further comprise: a third actuator having adriving axis in a third direction which is perpendicular to the firstdirection and the second direction; and a third slider that couples thevibration table with the third actuator to be slidable in the firstdirection and the second direction. In this configuration, the firstslider may couple the vibration table with the first actuator to beslidable in the second direction and the third direction, and the secondslider may couple the vibration table with the second actuator to beslidable in the first direction and the third direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an electrodynamic excitation device accordingto a first embodiment of the invention.

FIG. 2 is a plan view of the electrodynamic excitation device accordingto the first embodiment of the invention.

FIG. 3 is a block diagram of a drive system of the electrodynamicexcitation device according to the first embodiment of the invention.

FIG. 4 is a front view of a main body of a Z-axis actuator according tothe first embodiment of the invention.

FIG. 5 is a plan view of the main body of the Z-axis actuator accordingto the first embodiment of the invention.

FIG. 6 is a vertical cross section of the main body of the Z-axisactuator according to the first embodiment of the invention.

FIG. 7 is an enlarged plan view illustrating a portion around avibration table of the Z-axis actuator according to the first embodimentof the invention.

FIG. 8 is a cross section of a linear guide used in the electrodynamicexcitation device according to the first embodiment of the invention.

FIG. 9 is a cross section taken by a line I-I in FIG. 8.

FIG. 10 is a front view of an electrodynamic excitation device accordingto a second embodiment of the invention.

FIG. 11 is a plan view of the electrodynamic excitation device accordingto the second embodiment of the invention.

FIG. 12 is a side view of the electrodynamic excitation device accordingto the second embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereafter, embodiments of the invention are described with reference tothe accompanying drawings.

First Embodiment

Hereafter, an electrodynamic triaxial excitation device 1 (hereafter,simply referred to as an excitation device 1) according to a firstembodiment of the invention is described with reference to FIGS. 1 to 9.FIGS. 1 and 2 are a front view and a plan view of the excitation device1, respectively. FIG. 3 is a block diagram illustrating a generalconfiguration of a drive system of the excitation device 1. In thefollowing explanation of the first embodiment, the left and rightdirection in FIG. 1 is defined as a X-axis direction (the rightwarddirection is a positive direction of X-axis), a direction perpendicularto the paper face of FIG. 1 is defined as a Y-axis direction (thedirection from the front side to the back side of the paper face of FIG.1 is a positive direction of Y-axis), and an up and down direction inFIG. 1 is defined as a Z-axis direction (the upward direction is apositive direction of Z-axis). The Z-axis direction is a verticaldirection, and each of the X-axis direction and the Y-axis direction isa horizontal direction.

As shown in FIGS. 1 and 2, the excitation device 1 includes a vibrationtable 400 to which a test piece (not shown) is attached, three actuators(an X-axis actuator 100, a Y-axis actuator 200 and a Z-axis actuator300) which vibrate the vibration table 400 in X-axis, Y-axis and Z-axisdirections, respectively, and a device base 50 which supports theactuators 100, 200 and 300. The actuators 100, 200 and 300 areelectrodynamic linear motion actuators each having a voice coil motor,and respectively include main bodies 101, 201 and 301, and covers 103,203 and 303 covering movable parts (described later) protruding from therespective main bodies 101, 201 and 301. The vibration table 400 iscoupled to the actuators 100, 200 and 300 via respective biaxial sliders(a YZ slider 160, a ZX slider 260 and a XY slider 360). The excitationdevice 1 is able to vibrate the test piece attached to the vibrationtable 400 in the three axes directions which are perpendicular to eachother, by driving the vibration table 400 with the actuators 100, 200and 300.

The device base 50 is formed such that horizontally arranged bottom andtop plates and 56 are coupled to each other with a plurality of wallplates 58. The actuators 100, 200 and 300 are fixed to the top plate 56of the device base 50 with a pair of fixing blocks 110, a pair of fixingblocks 210 and a pair of fixing blocks 310, respectively. An opening 57is formed in the top plate 56, and the lower portion of the Z-axisactuator 300 is accommodated in the device base 50 via the opening 57.With this configuration, the excitation device 1 is formed to have a lowheight. In order to suppress transmission of the vibration from thedevice base 50 to an installation floor F, a plurality of antivibrationmounts 52 are attached to the lower surface of the bottom plate 54.

As shown in FIG. 3, the drive system of the excitation device 1 includesa control unit 10 which totally controls operation of the excitationdevice 1, a measurement unit 20 which measures vibration of thevibration table 400, a power source unit 30 which supplies electricpower to the control unit 10, and an input unit 40 which receives a datainput from a user or an external device. The measurement unit 20includes a triaxial vibration pickup 21 attached to the vibration table400. The measurement unit 20 amplifies a signal (e.g., a speed signal)outputted by the triaxial vibration pickup 21 to convert the signal to adigital signal, and transmits the digital signal to the control unit 10.The triaxial vibration pickup 21 detects the vibrations in the X-axis,Y-axis and Z-axis directions of the vibration table 400 independently.Based on an excitation waveform inputted from the input unit 40 and thesignal from the measurement unit 20, the control unit 10 is able tovibrate the vibration table 400 at desired amplitude and frequency bycontrolling the magnitude and the frequency of AC currents to beinputted to drive coils (described later) of the actuators 100, 200 and300. Furthermore, based on the signal of the triaxial vibration pickup21, the measurement unit 20 calculates various parameters (e.g., speed,acceleration, amplitude, power spectrum) indicating a vibrating state ofthe vibration table 40, and transmits the parameters to the control unit10.

Next, configurations of the actuators 100, 200 and 300 are explained.Since each of the X-axis actuator 100 and the Y-axis actuator 200 hasthe same configuration as that of the Z-axis actuator 300, except thatan air spring is not provided in the Z-axis actuator 300, the Z-axisactuator 300 is explained in detail as a representative example of theactuators.

FIGS. 4, 5 and 6 are a front view, a plan view and a vertical crosssection of the main body 301 of the Z-axis actuator 300. The main body301 includes a fixed part 320 having a cylindrical body 322, and amovable part 350 accommodated in a cylinder of the cylindrical body 322.The movable part 350 is provided to be movable in the Z-axis direction(the up and down direction in FIGS. 4 and 6) with respect to the fixedpart 320. The movable part 350 includes a cylindrical movable frame 356,and a drive coil 352 disposed to be substantially coaxial with themovable frame 356. The drive coil 352 is attached to a lower end of themovable frame 356 via a drive coil holding member 351. The movable frame356 is configured such that an upper portion thereof is formed in ashape of a cylinder and a lower portion thereof is formed in a shape ofa frustum cone whose side face is gently inclined so that the outerdiameter becomes larger toward the lower side. Furthermore, as shown inFIG. 6, the movable frame 356 includes a rod 356 a extending along thecenter axis, a top plate 356 b disposed to be perpendicular to thecenter axis, an intermediate plate 356 c and a bottom plate 356 d. Thetop plate 356 b, the intermediate plate 356 c and the bottom plate 356 dare coupled to each other by the rod 356 a. The rod 356 a is formed tofurther extend downward from the bottom plate 356 d. Furthermore, thevibration table 400 is attached to the top plate 356 b via the XY slider360.

In the cylindrical body 322 of the fixed part 320, a cylindrical innermagnet 326 is fixed to be coaxial with the cylindrical body 322. Theinner magnet 326 has an outer diameter smaller than the inner diameterof the drive coil 352, and the drive coil 352 is disposed in a gapsandwiched between the outer circumferential surface of the inner magnet326 and the inner circumferential surface of the cylindrical body 322.Each of the cylindrical body 322 and the inner magnet 326 is made ofmagnetic material. In the cylinder of the inner magnet 326, a bearing328 which slidably supports the rod 356 a in the Z-axis direction isfixed.

On the inner circumferential surface 322 a of the cylindrical body 322,a plurality of recessed parts 322 b are formed, and, in each recessedpart 322 b, an excitation coil 324 is accommodated. When a DC current(the excitation current) flows through the excitation coil 324, amagnetic field indicated by an arrow A is produced in the radialdirection of the cylindrical body 322 in a portion where the innercircumferential surface 322 a of the cylindrical body 322 is situated toclosely face the outer circumferential surface of the inner magnet 326.When the current is supplied in this state, a Lorentz force is caused inthe axial direction of the drive coil 352, i.e., in the Z-axisdirection, and the movable part 350 is driven in the Z-axis direction.

In the cylinder of the inner magnet 326, an air spring 330 isaccommodated. The lower end of the air spring 330 is fixed to the fixedpart 320, and the rod 356 a is fixed to the upper end of the air spring330. The air spring 330 supports the movable frame 356 via the rod 356 afrom the lower side. That is, the weight (the static load) of themovable part 350, the XY slider 360 supported by the movable part 350,the vibration table 400 and the test piece is supported by the airspring 330. Therefore, by providing the air spring 330 for the Z-axisactuator 300, it becomes unnecessary to support the weight (the staticload) of the movable part 350, the vibration table 400 and etc. by thedriving force (Lorentz force) of the Z-axis actuator 300. Since it isonly required to provide the dynamic load to vibrate the movable part350, the driving current to be supplied to the Z-axis actuator 300(i.e., power consumption) is reduced considerably. Furthermore, sincethe drive coil 352 can be downsized thanks to the reduction of therequired driving force, it becomes possible to drive the Z-axis actuator300 at a high frequency. Furthermore, it becomes unnecessary to supply alarge DC component to the drive coil for supporting the weight of themovable part 350, the vibration table 400 and etc. Therefore, it becomespossible to employ a simple and compact circuit as the power source unit30.

When the movable part 350 of the Z-axis actuator 300 is driven, thefixed part 320 also receives a reaction force (the excitation force) inthe drive axis (Z-axis) direction. By providing the air spring 330between the movable part 350 and the fixed part 320, the exciting forcetransmitted from the movable part 350 to the fixed part 320 is reduced.As a result, for example, the vibration of the movable part 350 isprevented from being transmitted, as noise, to the vibration table 400via the fixed part 320, the device base 50 and the actuators 100 and200.

Next, a configuration of a movable part support mechanism 340 whichsupports the upper portion of the movable part 350 to be slidable in theaxis direction is explained. The movable part support mechanism 340includes guide frames 342, Z-axis runner blocks 344 and Z-axis rails346. To a side surface of a cylindrical upper portion of the movablepart 350 (the movable frame 356), four Z-axis rails 346 extending in theZ-axis direction are attached. On the upper surface of the fixed part320 (the cylindrical body 322), four guide frames 342 are fixed to haveconstant intervals (of 90°) along the outer circumferential surface ofthe cylindrical body 322. The guide frame 342 is a fixing member havinga cross section formed in a shape of a letter L enforced by a rib. To anupright part 342 u of each guide frame 342, the Z-axis runner block 344engaging with the Z-rail 346 is attached. The Z-axis runner block 344has a plurality of rotatable balls 344 b (described later), andconstitutes a Z-axis linear guide 345 of a ball bearing type, togetherwith the Z-axis rail 346. That is, the movable part 350 is supported,from the lateral side, by the four pairs of supporting mechanisms eachof which is formed of the guide frame 342 and the Z-axis linear guide345, so that the movable part 350 is not able to move in the X-axis andY-axis directions. As a result, occurrence of crosstalk by the vibrationof the movable part 350 in the X-axis and Y-axis directions can beprevented. Furthermore, through use of the Z-axis linear guide 345, themovable part 350 is able to smoothly move in the Z-axis direction.Furthermore, since the movable part 350 is supported to be movable onlyin the Z-axis direction by the bearing 328 also in the lower portion asdescribed above, the movable part 350 is not able to move in the X-axisand Y-axis directions. As a result, the vibration of the movable part350 in the X-axis and Y-axis directions becomes hard to occur.

In the case where the movable frame 356 and the guide frame 342 arecoupled to each other with the Z-axis linear guide 345, it is alsopossible to employ a configuration where the Z-axis rail 346 is attachedto the guide frame 342 fixed to the fixed part 320 and the Z-axis runnerblock 344 is attached to the movable frame 356. However, in thisembodiment, the Z-axis rail 346 is attached to the movable frame 356 andthe Z-axis runner block 344 is attached to the guide frame 342, incontrast to the above described configuration. By employing such aconfiguration in this embodiment, unnecessary vibration can besuppressed. This is because the Z-axis rail 346 is lighter than theZ-axis runner block 344, the Z-axis rail 346 is longer than the Z-axisrunner block 344 in the drive direction (Z-axis direction) (therefore,mass per a unit of length is small), the mass distribution in the drivedirection is uniform, and therefore the fluctuation of the massdistribution caused when the Z-axis actuator 300 is driven is smaller inthe case where the Z-axis rail 346 is attached to the movable side andas a result the vibration caused in accordance with the fluctuation ofthe mass distribution can be suppressed to a low level. Furthermore,since the barycenter of the Z-axis rail 346 is lower (i.e., the distancefrom the installation surface to the barycenter is shorter) than thebarycenter of the Z-axis runner block 344, the moment of inertia becomessmaller in the case where the Z-axis rail 346 is fixed to the movableside. Accordingly, with this configuration, it becomes possible to setthe resonance frequency to be higher than the excitation frequency(e.g., 0 to 100 Hz), and thereby it becomes possible to preventdeterioration of the accuracy of excitation by resonance.

Hereafter, a configuration of the XY slider 360 which couples the Z-axisactuator 300 to the vibration table 400 is explained. FIG. 7 is a planview enlarging a portion around the vibration table 400. As shown inFIGS. 6 and 7, the XY slider 360 includes two Y-axis rails 362 a, fourY-axis runner blocks 362 b, four joint plates 364, four X-axis runnerblocks 366 b and two X-axis rails 366 b. The two Y-axis rails 362 aextending in the Y-axis direction are attached to the upper surface ofthe top plate 356 b. To the Y-axis rails 362 a, the two Y-axis runnerblocks 362 engaging with the Y-axis rail 362 are attached to be slidablealong the Y-axis rails 362 a. The two X-axis rails 366 a extending inthe X-axis direction are attached to the lower surface of the vibrationtable 400. To the X-axis rails 366 a, the two X-axis runner blocks 366 bengaging with the X-rail 366 a are attached to be slidable along theX-axis rails 366 a. The X-axis runner blocks 366 b are coupled torespective ones of the Y-axis runner blocks 362 b via the respectivejoint plates 364. Specifically, one of the X-axis runner blocks 366 bengaging with one X-axis rail 366 a is coupled to one of the Y-axisrunner blocks 362 b engaging with one Y-axis rails 362 a, and the otherX-axis runner block 366 b is coupled to one of the Y-axis runner blocks362 b engaging with the other Y-axis rail 362 a. That is, each X-axisrail 366 a is coupled to the Y-axis rail 362 a via the X-axis runnerblock 366 b and the Y-axis runner block 362 b coupled with the jointplate 364. With this configuration, the vibration table 400 is coupledto the movable part 350 of the Z-axis actuator 300 to be slidable in theX-axis and Y-axis directions.

As described above, by coupling the Z-axis actuator 300 to the vibrationtable 400 via the XY slider 360 to be slidable in the X-axis and Y-axisdirections by a very small force, the vibration components of thevibration table 40 in the X-axis and Y-axis directions are nottransmitted to the Z-axis actuator 300 even when the vibration table 400is vibrated in the X-axis and Y-axis directions by the X-axis actuator100 and the Y-axis actuator 200. Furthermore, even when the vibrationtable 400 is vibrated in the Z-axis direction by the Z-axis actuator300, the vibration component of the vibration table 400 in the Z-axisdirection is not transmitted to the X-axis actuator 100 and the Y-axisactuator 200. Accordingly, excitation in a low degree of crosstalk canbe realized.

Hereafter, a configuration of the YZ slider 160 which couples the X-axisactuator 100 to the vibration table 400 is explained. The YZ slider 160includes two Z-axis rails 162 a, two Z-axis runner blocks 162 b, twojoint plates 164, two Y-axis runner blocks 166 b and one Y-axis rail 166a. The two Z-axis rail 162 a extending in the Z-axis direction areattached to a top plate 156 b of the movable frame of the X-axisactuator 100. To the Z-axis rail 162 a, the Z-axis runner block 162 bengaging with the Z-axis rail 162 a is attached to be slidable along theZ-axis rail 162 a. Furthermore, to a side surface of the vibration table400 facing the X-axis actuator 100, the Y-axis rail 166 a extending inthe Y-axis direction is attached. The Y-axis runner block 166 b iscoupled to one of the Z-axis runner blocks 162 b via one of the Z-axisrunner blocks 162 b. That is, the Y-axis rail 166 a is coupled to theZ-axis rail 162 a via the Y-axis runner block 166 b and the Z-axisrunner block 162 b coupled by the joint plate 164. With thisconfiguration, the vibration table 400 is coupled to the movable part150 of the X-axis actuator 100 to be slidable in the Y-axis and Z-axisdirections.

As described above, by coupling the X-axis actuator 100 to the vibrationtable 400 via the YZ slider 160 to be slidable in the Y-axis and Z-axisdirections at a small degree of frictional force, the vibrationcomponents of the vibration table 400 in the Y-axis and Z-axisdirections are not transmitted to the X-axis actuator 100 even when thevibration table 400 is vibrated by the Y-axis actuator 200 and theZ-axis actuator in the Y-axis and Z-axis directions. Furthermore, evenwhen the vibration table 400 is vibrated in the X-axis direction by theX-axis actuator 100, the vibration component of the vibration table 400in the X-axis direction is not transmitted to the Y-axis actuator 200and the Z-axis actuator 300. As a result, excitation in a low degree ofcrosstalk can be realized.

The ZX slider 260 which couples the Y-axis actuator 200 to the vibrationtable 400 also has the same configuration as that of the YZ slider 160,and the vibration table 400 is coupled to the movable part of the Y-axisactuator 200 to be slidable in the Z-axis and X-axis directions.Therefore, even when the vibration table 400 is vibrated by the Z-axisactuator 300 and the X-axis actuator 100 in the Z-axis and X-axisdirections, the vibration components of the vibration table 400 in theZ-axis and X-axis directions are not transmitted to the Y-axis actuator200. Furthermore, even when the vibration table 400 is vibrated in theY-axis direction by the Y-axis actuator 200, the vibration component ofthe vibration table 400 in the Y-axis direction is not transmitted tothe Z-axis actuator 300 and the X-axis actuator 100. As a result,excitation in a low degree of crosstalk can be realized.

As described above, the actuators 100, 200 and 300 are able toaccurately excite the vibration table 400 in the drive axis directionswithout interfering with each other. Furthermore, since each of theactuators 100, 200 and 300 is supported by the guide frame and thelinear guide such that the movable part thereof is slidable only in thedrive direction, vibration in the non-drive direction is hard to occur.Therefore, vibration in the non-drive direction which is not beingcontrolled is not applied to the vibration table 400. As a result, thevibration of the vibration table 400 in each drive axis direction can beaccurately controlled by driving of the corresponding one of theactuators 100, 200 and 300.

Next, a configuration of a liner guide mechanism (a rail and a runnerblock) used in each of the movable part support mechanism 340, the YZslider 160, the ZX slider 260 and the XY slider 360 is explained, takingthe Z-axis linear guide mechanism 345 (the Z-axis runner block 344 andthe Z-axis rail 346) used in the movable part support mechanism 340 asan example. The other rails and the runner blocks are also configured tohave the same configurations as those of the Z-axis runner block 344 andthe Z-axis rail 346, respectively.

FIG. 8 is a cross-sectional view of the Z-axis rail 346 and the Z-axisrunner block 344 of the movable part support mechanism 340, viewed bycutting along a plane (i.e., an XY plane) perpendicular to the longeraxis of the Z-axis rail 346. FIG. 9 is an I-I cross section of the FIG.8. As shown in FIGS. 8 and 9, a recessed part is formed on the Z-axisrunner block 344 to surround the Z-axis rail 346, and two pairs ofgrooves 344 a and 344′a are formed on the recessed part to extend in theaxial direction of the Z-axis rail 346. In each of the grooves 344 a and344 a′, a plurality of stainless steel balls 344 b and a resin retainer344 r are accommodated. The retainer 344 r has a plurality of spacers344 rs disposed between the balls 344 b, and a pair of bands 344 rbcoupling the plurality of spaces 344 rs. The balls 344 b are held inspaces surrounded by the plurality of spacers 344 rs and the band 344rb. Grooves 346 a and 346 a′ are formed on the Z-axis rail 346 atpositions facing the grooves 344 a and the 344 a′ of the Z-axis runnerblock 344, respectively, and the balls 344 b and the retainer 344 r aresandwiched between the groove 344 a and the groove 346 a or between thegroove 344 a′ and the groove 346 a′. Each of the grooves 344 a, 344 a′,346 a and 346 a′ has a cross section formed in a shape of an arc, andthe curvature radius of the arc is the same as the radius of the ball344 b. Therefore, the ball 344 b closely contacts each of the grooves344 a, 344 a′, 346 a and 346 a′ with almost no play.

In the Z-axis runner block 344, two pairs of ball saving paths 344 c and344 c′ are provided to extend in substantially parallel with the grooves344 a and 344 a′. As shown in FIG. 9, the groove 344 a′ and the savingpath 344 c′ are connected by U-shaped paths 344 d′ at both ends, and acircular path for circulating the balls 344 b and the retainer 344 r isformed by the groove 344 a′, the groove 346 a′, the saving path 344 c′and the U-shaped paths 344 d. Similarly, a circular path is also formedby the groove 344 a, the groove 346 a and the saving path 344 c.

Therefore, when the Z-axis runner block 344 moves with respect to theZ-axis rail 346, the plurality of balls 344 b circulate, together withthe retainer 344 r, while rotating along the grooves 344 a and 346 a andthe grooves 344 a′ and 346 a′. Therefore, even when a large load isapplied in a direction other than the axial direction of the rail, theZ-axis runner block 344 can be smoothly moved along the Z-axis rail 346because the Z-axis runner block 344 can be supported by the plurality ofballs 344 b and resistance in the axial direction of the rail can bekept at a low level due to rotations of the balls 344 b. An innerdiameter of each of the saving paths 344 c and 344 c′ and the U-shapedpaths 344 d and 344 d′ is slightly larger than the diameter of the ball344 b. For this reason, the frictional force caused between the ball 344b and each of the saving paths 344 c and 344 c′ and the U-shaped paths344 d and 344 d′ is very small, and the circulating motion of the balls344 b are not hampered by the frictional force.

By providing the spacers 344 rs of the retainer 344 r having a lowdegree of rigidity between the balls 344 b, wearing and loss of oil filmwhich would be caused by direct contact of the balls at one point can beavoided, the frictional resistance is lowered, and as a result thelifetime can be increased considerably.

Each of the X-axis actuator 100 and the Y-axis actuator 200 also has amovable part support mechanism (not shown). The movable part of theX-axis actuator 100 is supported by a guide frame from the both sides inthe two directions (Y-axis and Z-axis directions) which areperpendicular to the drive direction (X-axis). Similarly, the movablepart of the Y-axis actuator 200 is supported by a guide frame from theboth sides in the two directions (Z-axis and X-axis directions) whichare perpendicular to the drive direction (Y-axis). Each of the X-axisactuator 100 and the Y-axis actuator 200 is placed such that the longerside direction of the movable part is oriented horizontally. Therefore,in a conventional actuator not provided with a movable part supportmechanism, a movable part is supported only by a rod in a state of acantilever type, and therefore a tip side (the vibration table 400 side)of the movable part falls downward due to its own weight and this causesfactors of friction and undesired vibration during the driving. Bycontrast, in this embodiment, the movable part of each of the X-axisactuator 100 and the Y-axis actuator 200 is supported from the lowerside by the guide frame, such a problem is solved.

Second Embodiment

Hereafter, an electrodynamic biaxial excitation device 1000 (hereafter,simply referred to as an “excitation device 1000”) according to a secondembodiment of the invention is explained with reference to FIGS. 10 to12. In the excitation device 1 according to the above described firstembodiment, the main bodies 101, 201 and 301 (specifically, the fixedpart) of the actuators are firmly supported by the device base 50 viathe fixing blocks 110, 210 and 310, respectively. Therefore, vibrationof the fixed part of one actuator may be transmitted to the vibrationtable 400 via the device base 50 and the other of the actuators 100, 200and 300, and may becomes a noise component of the vibration. Asdescribed later, the excitation device 1000 according to the secondembodiment is configured such that a fixed part of each actuator issupported by a device base via an air spring in the drive direction inwhich strong vibration is caused. Therefore, according to the secondembodiment, excitation with a still higher degree of accuracy can berealized.

FIGS. 10, 11 and 12 are a front view, a plan view and a side view(showing a left side in FIG. 10) of the excitation device 1000,respectively. In the following explanation about the second embodiment,the rightward direction in FIG. 10 is defined as a positive direction ofthe X-axis, the direction pointing from the front side to the back sideof the paper face of FIG. 10 is defined as the positive direction of theY-axis, and the upward direction in FIG. 10 is defined as the positivedirection of the Z-axis. The Z-axis direction is a vertical direction,and each of the X-axis and Y-axis directions is a horizontal direction.To elements which are the same or substantially the same as those of thefirst embodiment, the similar reference numbers are assigned, anddetailed explanations thereof are omitted.

The excitation device 1000 is configured to be able to vibrate a testpiece (not shown) in the two directions, i.e., the X-axis direction andthe Z-axis direction, and includes a vibration table 1400 to which thetest piece is attached, two actuators (an X-axis actuator 1100 and aZ-axis actuator 1300) which vibrate the vibration table 1400 in theX-axis and Z-axis directions, respectively, a device base 1050 whichsupports the actuators 1100 and 1300. One side surface of the vibrationtable 1400 is coupled to the X-axis actuator 1100 via a Z-axis slider1160, and the lower surface of the vibration table 1400 is coupled tothe Z-axis actuator 1300 via an X-axis slider 1360. As in the case ofthe excitation device 1 of the first embodiment, the excitation device1000 also includes a biaxial vibration pickup, a measurement unit, acontrol unit, an input unit and a power source unit (not shown). Theinner configuration of the actuators 1100 and 1300 and the configurationof the device base 1050 are the same as those of the excitation device 1of the first embodiment.

The X-axis actuator 1100 is fixed to a top plate 1056 of the device base1050 by a support unit 1110. The support unit 1110 includes a pair offixing blocks 1112 each having an inverted T-shape attached to the topplate 1056, a pair of movable blocks 1118 each having a rectangularplate shape respectively attached to the both side faces of a fixed part1120 of the X-axis actuator 1100, and a pair of linear guides 1114 whichslidably couple the fixing block 1112 and the movable block 1118 in theX-axis direction. Each linear guide 1114 includes a rail 1114 a which isattached to the upper surface of a foot part 1112 b of the invertedT-shape fixed block 1112 to extend in the X-axis direction, and a pairof runner blocks 1114 b which is attached to the lower surface of themovable block 1118 to engage with the rail 1114 a. On a side surface ofthe foot part 1112 b of the fixed block 1112 on the positive side of theX-axis, a branch part 1112 a extending upward is fixed. The side surfaceof the movable block 1118 on the positive side of the X-axis is coupledto the branch part 1112 a of the fixed block 1112 via a pair of airsprings 1116 arranged in the up and down direction. Thus, the fixed part1120 of the X-axis actuator 1100 is flexibly supported, by the fixedpart support mechanism including the linear guide 1114 and the airsprings 1116, in the drive direction (X-axis direction), with respect tothe fixed block 1112 (i.e., the device base 1050). Therefore, the strongreaction force (the excitation force) applied to the fixed part 1120 inthe X-axis direction during driving of the X-axis actuator 1100 is notdirectly transmitted to the device base 1050, and is transmitted to thedevice base 1050 after the high frequency component thereof is largelyreduced by the air springs 1116. Therefore, the vibration noisetransmitted to the vibration table 1400 is reduced considerably.

The Z-axis actuator 1300 is fixed to the top plate 1056 of the devicebase 1050 by a pair of support units 1310 arranged on the both sidesthereof in the Y-axis direction. The lower portion of the Z-axisactuator 1300 is accommodated in the device base 1050 through an opening1057 provided in the top plate 1056 of the device base 1050. Eachsupport unit 1310 includes a movable block 1318, a pair of angles 1312and a pair of linear guides 1314. The movable block 1318 is a supportmember attached to the side surface of a fixed part 1320 of the Z-axisactuator 1300. The pair of angles 1312 is disposed to face the bothsides of the movable block 1318 in the X-axis direction, and is attachedto the upper surface of the top plate 1056. The both sides of themovable block 1318 in the X-axis direction are coupled to the respectiveangles 1312 to be slidable in the Z-axis direction by the pair of linearguides 1314. The movable block 1318 includes an angle block 1318 a, aflat plate block 1318 b and a pair of T-shaped blocks 1318 c. Oneattachment surface of the L-shaped angle block 1318 a is fixed to theside surface of the fixed part 1320 of the Z-axis actuator 1300. On theother attached surface of the angle block 1318 a oriented upward, theflat plate block 1318 b having a rectangular flat shape extending in theX-axis direction is fixed at the central portion in the longer sidedirection of the flat plate block 1318 b. To the upper surfaces at theboth ends in the X-axis direction of the flat plate block 1318 b, footparts 1318 d of the T-shaped blocks 1318 c are attached. To theattachment surfaces of the T-shaped blocks 1318 c (the both sidesurfaces in the X-axis direction of the movable block 1318), the rails1314 a of the linear guides 1314 extending in the Z-axis direction areattached, respectively. The runner block 1314 b which faces and engageswith the rail 1314 a is attached to each angle 1312. At the both ends inthe X-axis direction of the angle block 1318 a, a pair of air springs1316 is disposed to be sandwiched between the flat plate block 1318 band the top plate 1056 of the device base 1050, and the movable block1318 is supported by the top plate 1056 via the pair of air springs1316. Thus, as in the case of the X-axis actuator 1100, the Z-axisactuator 1300 is also flexibly supported, in the drive direction (Z-axisdirection), with respect to the device base 1050 via the fixed partsupport mechanism including the liner guide 1314 and the air springs1316. Therefore, the strong reaction force (the excitation force)applied to the fixed part 1320 during driving of the Z-axis actuator1300 is not directly transmitted to the device base 1050, and the highfrequency component thereof is largely reduced by the air springs 1316.As a result, the vibration noise transmitted to the vibration table 1400is reduced largely.

The forgoing is the explanations about the embodiments of the invention.It is understood that embodiments of the present invention are notlimited to the above described embodiments, and can be varied within thescope of the invention.

For example, the excitation device 1 of the first embodiment is anexample in which the invention is applied to an actuator of anelectrodynamic triaxial excitation device, and the excitation device1000 of the second embodiment is an example in which the invention isapplied to an actuator of an electrodynamic biaxial excitation device;however, the invention may also be applied to an electrodynamicsingle-axis excitation device.

In the above described first embodiment, the movable part 350 of theelectrodynamic actuator 300 is supported, from the lateral side, by thefour movable part support mechanism 340 disposed to have approximatelyconstant intervals around the axis of the cylindrical body 322. However,the invention is not limited to such a configuration. In anotherembodiment, the movable part may be supported, from the lateral side, bytwo or more (preferably more than three) movable part support mechanismsarranged to have approximately constant intervals around the axis of thecylindrical body.

In the above described first embodiment, the runner block is fixed tothe upper surface of the cylindrical body 322 via the fixed guide frame342; however, the runner block may be directly fixed to the innercircumferential surface of the cylindrical body 322.

In the above described second embodiment, the air springs 1116 and 1316are used as buffering members for reducing the vibration of the fixedpart support mechanism; however, various members, such as another typeof spring or an elastic body (a rubber cushion) having the vibrationabsorption function, or a damper device using an electromagneticreaction force, may be used.

The linear actuator according to the embodiment of the invention may beused for a device other than the excitation device. For example, theactuator according to the embodiment may be used for a universal testdevice (material test device) for performing a tension and compressiontest, an accurate positioning device or a jack device.

In the above described embodiment, the actuator is controlled using thespeed of the vibration table as a control variable; however, control maybe performed by using the displacement or the acceleration of thevibration table as a control variable. In place of the vibration table,the displacement, the speed or the acceleration of the test piece or themovable part of the actuator may be used as a control variable to driveand control the actuator.

What is claimed is:
 1. A linear actuator, comprising: a base; a fixedpart support mechanism attached to the base; a fixed part elasticallysupported by the fixed part support mechanism; and a movable part drivento reciprocate in a predetermined drive direction with respect to thefixed part, wherein the fixed part support mechanism comprises: amovable block attached to the fixed part; a linear guide that couplesthe movable block with the base to be slidable in the predetermineddrive direction; and an elastic member that is disposed between the baseand the movable block and prevents transmission of a high frequencycomponent of vibration in the predetermined drive direction.
 2. Thelinear actuator according to claim 1, wherein the elastic membercomprises an air spring.
 3. The linear actuator according to claim 1,further comprising a fixing block fixed to the base, wherein at leastone of the linear guide and the elastic member is attached to the basevia the fixing block.
 4. The linear actuator according to claim 1,wherein: the movable block is provided as a pair of movable blocks; andthe pair of movable blocks is attached to both side surfaces of thefixed part to sandwich an axis of the fixed part therebetween.
 5. Thelinear actuator according to claim 1, wherein at least a part of themovable part is accommodated in a cylindrical hollow part of the fixedpart, thereby forming the linear actuator as an electrodynamic actuator,the linear actuator further comprising: a plurality of movable partsupport mechanisms that support the movable part from a lateral side toenable the movable part to reciprocate in an axial direction of thefixed part, wherein each of the plurality of movable part supportmechanisms comprises: a rail attached to a side surface of the movablepart to extend in the predetermined drive direction; and a runner blockattached to the fixed part to engage with the rail, wherein theplurality of movable part support mechanisms are arranged to haveapproximately constant intervals therebetween around an axis of thefixed part.
 6. The linear actuator according to claim 5, wherein: theplurality of movable part support mechanisms are two pairs of movablepart support mechanisms; and the movable part is disposed to besandwiched between the two pairs of movable part support mechanisms intwo directions which are perpendicular to each other.
 7. The linearactuator according to claim 5, wherein: the linear actuator ishorizontally disposed in a state where the axis of the fixed part isoriented in a horizontal direction; and one of the plurality of movablepart support mechanisms is disposed under the axis of the fixed part. 8.The linear actuator according to claim 5, wherein: the movable partcomprises a rod extending along the axis of the fixed part to protrudefrom one end of the movable part; and the fixed part comprises a bearingwhich supports the rod to be movable in the axial direction of the fixedpart.
 9. An excitation device, comprising: at least one linear actuatoraccording to claim 1; and a vibration table coupled to the movable partof the at least one linear actuator.
 10. The excitation device accordingto claim 9, wherein; the at least one linear actuator comprises twolinear actuators; one of the two linear actuators is a first actuatorhaving a driving axis in a first direction; and the other of the twolinear actuators is a second actuator having a driving axis in a seconddirection perpendicular to the first direction, wherein the excitationdevice further comprises: a first slider that couples the vibrationtable with the first actuator to be slidable in the second direction;and a second slider that couples the vibration table with the secondactuator to be slidable in the first direction.
 11. The excitationdevice according to claim 10, further comprising: a third actuatorhaving a driving axis in a third direction which is perpendicular to thefirst direction and the second direction; and a third slider thatcouples the vibration table with the third actuator to be slidable inthe first direction and the second direction, wherein: the first slidercouples the vibration table with the first actuator to be slidable inthe second direction and the third direction; and the second slidercouples the vibration table with the second actuator to be slidable inthe first direction and the third direction.